Contact index system



April 28, 1964 J. H. REESE 3,130,537

CONTACT INDEX SYSTEM Filed Oct. 20, 1961 2 Sheets-Sheet 1 INVENTOR hmesEReese,

ATTORNEYS A ril 23, 1964 'J. H. REESE 3,130,537

CONTACT INDEX SYSTEM Filed Oct. 20, 1961 2 Sheets-Sheet 2 INVENTOR ATTORNEYS United States Patent 3,130,537 CUNTACT INDEX SYSTEM James H. Reese, Mannheim, Pa., assignor to Hamilton Watch Company, Lancaster, Pa, a carporation of Pennsylvania Filed Oct. 20, 1961, Ser. No. 146,639 21 Claims. (til. 58-28) This invention relates to battery operated electric Watches and more particularly relates to an improved contact and index system for such Watches.

In electric wrist watches of the moving coil type which have been proposed and in the commercial electric wrist watch of the assignee of this application, it has been customary to provide periodic energization to the coil by means of some type of spring-type commutating system. One such system is illustrated in assignees patent to J. A. Van Horne et al., No. 2,806,908. The proper operation of this type of contact system is absolutely essential to the successful performance of the watch, and it has been found that some criticality of adjustment exists.

In this type of electric watch, the balance wheel serves as the source of motive power and it is necessary to provide an indexing mechanism which receives power from the oscillating movement of the balance wheel and transforms these oscillations into rotary movement in one direction. Generally speaking, this has been accomplished by means of a toothed wheel which is advanced in steps by means of a periodic contact with a jewel member carried by the balance wheel.

According to the present invention, it has now been found that it is possible to entirely eliminate this type of syring-type contact system and to utilize the indexing function of the balance wheel to perform the switching operation during the time that it indexes without any requirement for the expenditure of additional energy. Because of the unique arrangement of the contact system, adjustment is entirely eliminated, thereby obviating the criticality previously mentioned. Fewer parts are required in that the entire spring-type contact system is done away with, thereby permitting a space reduction which makes possible a thinner watch movement. In addition to this, it is found that the contact which is obtained is more reliable than that which is possible with the spring-type contact system.

While at least one other worker in the horological field has previously proposed a combined index and contact system for an electrical timepiece, the nature of that proposal was such as to make it impractical for high quality timekeeping. One reason for this was a failure to provide a system wherein the friction entailed in opera tion was both minimized and stabilized. That is to say, the friction represented in the load which the train of the timepiece presents to the prime mover should not only be at a minimum but should also be maintained as uniform as possible during the life of the timepiece. If this latter requirement is not substantially met the result is a timepiece which is erratic in operation and incapable of keeping truly accurate time. A further requirement which presents itself in wrist watch construction is that of miniaturization, particularly in the thickness of the movement.

a Not only does this requirement rule out certain prior proposals as satisfactory answers to the contact-index problem, but it also presents further problems in insuring against erratic watch operation because of unwanted closure of the energizing circuit at undesired instants in the operation of the system.

The contact-index arrangement of the instant invention solves the foregoing problems in a manner presently to be explained and provides the first commercially successful contact-index system ever devised for an electric wrist watch.

It is accordingly a primary object of the present invention to provide an improved contact and index system for an electric watch.

It is another object of the invention to provide an improved contact and index system for an electric watch of the type utilizing an oscillating balance staff to impart one way motion to an index wheel wherein the energy required to advance the index wheel is also utilized to provide the periodic electrical contact.

It is another object of the invention to provide an improved contact and index mechanism for an electric watch wherein adjustment of the contact system is substantially eliminated.

It is still a further object of the invention to provide a contact index system which minimizes and stabilizes friction and which provides positive assurance against unwanted contact while utilizing a minimum number of parts.

It is another object of the invention to provide an electric watch that is very nearly self-starting and can be started by a simple movement of the watch.

It is another object of the invention to provide an improved contact and index system for an electric Watch utilizing fewer parts than were heretofore found necessary.

It is still another object of the present invention to provide an improved contact index system for an electric watch which permits a reduction in the size of the watch movement to provide a thinner watch.

It is a still further object of the invention to provide an improved contact and index system which produces more reliable contact than that obtainable heretofore.

It is a further object of the invention to provide an improved contact and indexing system using a unique electrical circuit which avoids use of the train of the watch as a part thereof and which permits the use of jewel bearings for both the balance and index assemblies.

It is a still further object and advantage of the invention to provide an improved contact and index system using a unique electrical circuit which utilizes as a component part thereof an index assembly having one part in electrical contact with the watch train and another part insulated from the first part but periodically connected in the energizing circuit of the watch.

It is another object of the invention to provide a unique and improved index assembly for an electric watch.

These and further objects and advantages of the present invention will become more apparent upon reference to the following specification and claims, and appended drawings wherein:

FIGURE 1 is a partial vertical section of an electric watch showing the combined contact and index system of the present invention;

FIGURE 2 is a diagrammatic plan view showing the commencement of the index and contact cycle;

FIGURE 3 is a diagrammatic plan view showing the termination of the index and contact cycles;

FIGURE 4 is a diagrammatic plan view showing the return movement of the balance staff wherein neither contacting nor indexing occurs;

FIGURE 5 is a diagrammatic plan view showing another embodiment of the contact and index system;

FIGURE 6 is a diagrammatic plan view showing a still further embodiment of the contact and index system; and

FIGURE 7 is a partial view of the contact wheel showing the preferred shape of its teeth.

Referring to FIGURE 1, there is seen a pillar plate 10 which, in conjunction with a bridge (not shown), carries a balance stafl 12. The balance staff 12 carries a balance wheel (not shown) on which there is mounted a coil of the general type shown in the aforementioned Van Horn et al. Patent No. 2,806,908. Also attached to the balance staff 12 is an index roller 14 which may comprise a split collar of the type shown in the Van Horn et al. patent and which has friction fitted tierein a semi-cylindrical jewel pin 16. A contact plate it? is attached to the underside of the index roller 14 by any suitable insulating adhesive 17, such as an epoxy resin. The contact plate is accurately apertured to permit the jewel pin It) to pass therethrough.

Referring now to both FIGURES 1 and 2, a semicylindrical contact 18 depends from the contact plate 29. This contact can either be formed integrally with the contact plate (such as being formed as a swaged D-pin) or permanently joined therewith, for example, by welding. The semi-circular jewel pin 16 is disposed in a back-tobaek relationship with the contact 18 and may be attached thereto by any suitable adhesive. The diameter of the jewel pin is preferably larger than that of the contact for a reason presently to be described. A wire 24 is attached at one end to the coil and the other end is passed through a tube 25 which is carried by the roller 14. The tube 25 protects the wire 24 and also cooperates with a finger block (not shown) to provide motion limiting that forms no part of this invention. Electrical connection between wire 24 and the contact plate can be established in any desired manner, such as by solder 22 on the underside of the contact plate, the wire passing through an aperture in the contact plate.

Referring again to FIGURE 1, the pillar plate 10 and a train bridge 30 support jewel bearings 32 and 34 and an index assembly shown generally at 36. The jewel bearings contribute to a minimization of friction in the operation of the index assembly. This index assembly consists of an index pinion 38, staff 40, and index hub 42. I

Pinion 38 is in electrical and mechanical contact with the watch train (not shown). The staff it) is provided with an enlarged splined end 44 which is received in a recess 46 in the index hub 42. The spline 4-4 is provided to present a greater adhesive area to the epoxy resin 48 which is used to fill the recess 46. The spline may be in the form of V-shaped grooves although it will be appreciated that other spline shapes may be used so long as increased adhesion area is provided. Some type of tooth shape is preferable, however, because it provides a locking action with the adhesive. The index hub is provided with a pivot 45 which engages a contact pad 47 preferably composed of a precious or semi-precious alloy. The contact pad 47 is carried by a battery lead or spring 49 mounted below the pillar plate and secured thereto and electrically insulated therefrom in any suitable manner (not shown).

The index hub 42 carries a composite index wheel generally indicated at 56 consisting of an upper toothed alloy contact wheel 52 and a lower toothed wheel 54 mounted in abutting relationship. The wheel 54 is formed of a ferro-magnetic material and has a smaller diameter than the alloy contact wheel 52. These wheels are arranged so that their teeth are staggered in relation to one another, as best shown in FIGURES 2, 3 and 4. The ferro-magnetic Wheel 54 is basically a star wheel having teeth which are symmetric relative to a radius. The alloy contact wheel 52, on the other hand, has non-symmetric teeth which are best illustrated in FIGURE 7. Referring to that figure it will be seen that the teeth of the contact wheel 52 have undercut leading edges 6% which form an angle A with a radius through the leading edge of the tooth. In a preferred embodiment this angle is approximately 13 degrees. The lagging edge 62 of the tooth forms a much greater angle with respect to the radius through the leading edge and in a preferred embodiment forms an angle B of approximately 27 degrees. The significance of this tooth shape shall presently be discussed in greater detail. It is also to be noted that the tooth ends are rounded as shown at 61. The teeth of the alloy contact wheel extend into the path of movement of the jewel pin 16 and contact 18 carried by the balance staff 12, while the teeth of the lower magnetic index wheel 54 do not extend into this path.

A pair of small cylindrical index magnets 56 and 57 are frictionally carried by the pillar plate ltl beneath the index wheel 5% and act upon the magnetic index wheel 54 to pull the index assembly 36 downwardly so that the pivot 45 maintains continuous electric contact with the pad 47 on the battery lead 49. These magnets also serve a detent and drive function as presently will be explained. Although two such magnets are shown and preferred, it is to be understood that only one magnet is absolutely necessary to the operation of the present invention. The use of two such magnets insures a more positive and balanced pull-down of the pivot 45 and keeps it in firm contact with the pad 47.

In an electric watch of the type illustrated in Van Horn et al. Patent No. 2,806,908, it is desired to provide electric energization to the balance staif coil during a short period of time as the balance wheel and staff oscillate in one direction. During the return oscillation, it is ordinarily desired that no contact be made, although it is possible to design electric watches to operate with an impulse in both directions. The instant contact and index system is designed to transform the oscillating motion of the balance staff into one way rotary motion of the composite index wheel 50 and to cause a uniform limited time duration energization of the coil carried by the balance staff as the balance staff oscillates in one direction only. Indexing of the index wheel is carried out during this oscillation.

Referring to FIGURE 2, the balance staff is shown rotating or oscillating in the direction indicated by the arrow A and the jewel pin 16, contact 18, index wheel 50, and index magnet 56 are shown in greatly magnified size. The position of the index wheel 50 as seen in FIGURE 2 is the at rest position, wherein a tooth 64 of the magnetic index wheel 54 is centered over the index magnet 56 and is held by magnetic attraction between the magnet and the underlying magnetic tooth.

In a similar manner, the index magnet 57 is exerting a magnetic attraction on another one of the teeth 64 of the magnetic index wheel 54 on the other side of the index wheel.

In FIGURE 2, as the balance :stalf and index roller 14 rotate in the direction of the arrow A, the semi-circular edge of the contact 18' engages the rounded tip 61. of a tooth 58. This establishes a contact to one terminal of the balance stafi carried coil as follows: from the battery (not shown), through battery' lead 49, contact pad 47, pivot 45 of index hub 42', contact index wheel 52, contact 18, contact plate 2-0, and contact lead 24 to the coil. The other side of the coil is grounded to the watch frame by connection to the hairspring so that the only moving contacts are cont act index wheel 52 and contact 18.

As the balance staff 12 and index roller 14 rotate in the direction of the arrow A, the contact 1% drives the index wheel against the holding force of the index magnets 56 and 57 until the index wheel reaches the position as shown in FIGURE 3. In FIGURE 3, the contact 18,

index jewel 16, and index wheel 50 are shown in the position which represents the end of the contact period, whereupon further movement of the balance staff and index wheel in the direction of the arrow A causes termination of the contact between the tooth 58 and the semi-circular edge of the contact 18.

It is to be noted that in this position (FIGURE 3), the tooth '65 of the magnetic index wheel 54 is closer to the center of the index magnet 56 than is the tooth 64. Because of this, the magnetic attraction of the index magnet is stronger towards tooth 65 than tooth 64 and the index magnet thereby drives the index wheel 50 in the direction of the arrow B until the tooth 65 is centered over the index magnet as was the tooth 64 in FIGURE 2. It is to be understood that a similar action takes place between the index magnet 57 and another two teeth on the wheel 54. The index wheel has thereupon been indexed one tooth position, and contact to the coil has been established by the very movement that caused indexing.

Referring now to FIGURE 4, there is seen the return swing of the balance staff and index roller. With the index roller moving in this return direction, the jewel pin 16 will completely pass by the tooth 58 of the contact wheel previously advanced on the counterclockwise rotation of the balance staff as may be seen from FIGURE 2 and the comparison of the path of movement of the jewel pin indicated at C and the position of the tooth 59. Referring back to FIGURE 4, the jewel pin strikes the lagging edge 62 of a tooth in the relative position of the tooth 58 in FIGURE 2 and moves that tooth a slight amount in the counterclockwise direction.

The total movement of the index wheel 50 during this engagement with the jewel pin on back-swing is indicated by the arrow D in FIGURE 4 and is less than the movement of the index wheel on engagement with the contact during forward swing as indicated in FIGURES 2 and 3. The angular movement of the index wheel between the positions shown in FIGURES 2 and 3 is sufiicient to bring the tooth 64 into a position over the index magnet where the magnet draws the tooth forward. On the back swing, however, the movement is insufficient to cause the index magnet to advance the wheel and therefore when the jewel pin clears the tooth, the tooth merely returns to its position of rest over the magnet. As a result, the oscillation of the balance staff imparts a one-way rotary motion to the index wheel.

Reference to- FIGURE 2 will indicate that at the moment that contact is established between the contact 13 and the tooth 58 of contact wheel Sit to energize the coil in the driving system, the arcuate face of the contact 18 engages an arcuate portion 61 of tooth 58. As the contact 18 moves in the direction of the arrow A a rolling and sliding action occurs at the contacting surfaces but the distance that the contact 18 slides along the tooth 58 is maintained at a minimum. That is to say, the length of tooth edge that is subjected to a sliding action is minimized. This has been found to provide a minimum of friction and has been found to maintain the friction loss at a substantially uniform value as the timepiece ages. Such an arrangement has been found superior to a previously proposed converse arrangement wherein a contact pin establishes electrical contact with the edge 62 of the tooth and slides along that edge as electrical impulsing occurs. This latter arrangement has been found to cause pitting of the tooth surfaces with a resulting increase in friction that varies from tooth to tooth and detracts from the timekeeping ability of the watch.

While the undercut contact tooth shape shown in the drawings represents the most desirable arrangement it is possible to use tooth shapes wherein the leading edge of the tooth is generally radial. That is to say, it is desirable to use a contact wheel having teeth that are unsymmetric with relation to a radius through the tip of the tooth so that the angle A between the leading edge of the tooth and the radius is smaller than the angle C between the lagging edge of the tooth and the radius. According to the invention, contact should be made with a portion of the surface of the leading edge of the tooth. As previously stated, an undercut tooth is preferable but it is also within the comprehension of the invention that the leading edge of the contact tooth be generally radial and that the angle A in FIGURE 7 may even be a small angle on the other side of the radius. The words generally radial are intended to encompass this range.

It is to be noted in FIGURES 2-4 that the larger diameter of the jewel pin 16 as compared to the contact 18 places the radially outermost portion of the jewel pin at a greater distance from the balance staff axis than the radially outermost portion of the contact '18. This provides protection against inadvertent contact being es tablished during backswing and during possible jarring of the timepiece.

While the shape of the contact 1'3 in FIGURES 1-4 represents a preferred contact shape utilizing a generally semi-circular edge, it is possible to use different shapes of contact members. Thus, referred to FIGURE 5, there is shown another embodiment of the invention wherein similar reference numerals are provided for similar elements. According to this embodiment of the invention, the contact comprises a wedge having a cut-away diagonal edge 72 and a vertical end 74, in place of the semi-circular shaped contact of FIGURES 1-4.

Referring to FEGURE 6, there is shown another embodiment of the invention wherein the contact comprises a flat strip 76 to which the jewel pin is adhesively secured in place of the semi-circular shaped contact of FIGURES 1-4. It is believed apparent that the operation of these embodiments of the invention is substantially identical to that previously described in connection with the embodiment shown in FIGURES 1-4.

As a result of the above-described action of the contact and index system of this invention, it is possible to drive the index wheel of an electric watch from the oscillating motion of the balance staff while utilizing the same driving energy to provide electrical contact to a coil carried by the balance staff. The number of parts previously necessary to provide such contact is substantially reduced, there-by permitting the construction of a thinner electric watch movement.

In addition to this, the adjustment of the older type spring contact is eliminated, while at the same time the reliability of contact is improved. This type contact system also makes the watch of the present invention virtually self-starting, as a small movement of the watch will cause the contact 18 to contact one of the teeth on the contact wheel 52, thus initiating the operation of the watch. Once the watch has started, however, such movement of the watch will not disturb its operation due to the kinetic energy possessed by the various parts.

Other variations of the invention will become apparent to those skilled in the art and are intended to be included within the purview of the claims. As an example, it would be possible to substitute for the composite index wheel a magnetic wheel plated or coated with a high conductivity alloy. Alternatively, a magnetic wheel may be provided with high conductivity inserts. As an alternative to insulating the contacts from the index roller, the roller may be formed of an insulating material or may comprise an anodized metal.

This application is a continuation-in-part of my application Serial No. 792,014, filed February 9, 1959, now U.S. Patent No. 3,016,685, and entitled Electric Watch.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects .as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. A contact-indexing device for an electric watch comprising an oscillating balance staff, an index assembly including upper and lower portions, an insulating adhesive joining said portions, said upper portion carrying a pinion in electrical and mechanical contact with the gear train, the lower portion carrying a toothed index wheel adapted to be driven by said balance staff, a roller on said balance staff, an index and contact means mounted on said roller, and including an electrically insulating cam member and an electrically conducting contact, said index and contact means engaging said index wheel as said balance staff oscillates to impart step-by-step advancement thereto in one direction, said contact electrically engaging said index wheel during at least a portion of the oscillation which causes said advancement, said cam engaging said index wheel during the reverse oscillation which causes no net advancement, said cam member comprising an electrical insulating member having a curvate side and being engaged with said contact on another side, and means establishing contact with the lower end of said lower portion of said index assembly.

2. A contact-indexing device as set out in claim 1 wherein one edge of said cam member is disposed at a greater radial distance from said balance staff than the outermost edge of said contact.

3. A contact-indexing device as set out in claim 2 wherein said cam and said contact are each generally semi-cylindrical and disposed with their flat surfaces in engagement, the diameter of said cam being greater than the diameter of said contact.

4. A contact-indexing device as set out in claim 1 wherein said index wheel comprises a first magnetic gear wheel and a second non-magnetic gear wheel, said magnetic gear wheel having a diameter smaller than said nonmagnetic gear wheel, and magnetic means mounted to attract the teeth of said magnetic gear wheel.

5. An index assembly for an electric watch comprising a shaft carrying a pinion and having a pivot at one end thereof, a metal hub carrying a gear and having a pivot, the other end of said shaft being received in a recess in said hub and secured thereto by an insulating adhesive.

6. An index assembly as set out in claim 5 wherein said other end of said shaft is splined.

7. A contact-indexing device for an electric timepiece comprising an oscillating balance staff, contact-indexing means carried by said balance stalf, said contact-indexing means including electrically insulating and electrically conducting portions, an index assembly including shaft and hub portions, and insulating adhesive joining said portions, said shaft portion carrying a pinion in electrical and mechanical contact with the gear train of said time piece, said hub portion carrying a wheel having electrically conducting teeth which are non-symmetric relative to a radius through the outermost tip of the teeth, said teeth having a leading generally radial edge and a lagging edge, said electrically conducting portion of said contactindexing means being engageable with said leading edges of said teeth to establish electrical connection therewith as said balance staff oscillates, and means establishing electrical contact with t e lower end of said hub portion of said index assembly.

8. A contact-indexing device as set out in claim 7 wherein the leading edges of said teeth are undercut.

9. A contact indexing device as set out in claim 7 wherein the tips of said teeth are rounded and said electrically conducting portion of said contact-indexing means engages said rounded portion of said teeth.

10. An index assembly for an electric watch comprising a shaft portion carrying a pinion and having a pivot at one end thereof, a metal hub portion carrying contact and index means and having a pivot at one end, the other end of one of said portions being received in a recess in the other end of the other of said portions and secured thereto by an insulating adhesive.

11. A contact-indexing device for an electric watch comprising an oscillating balance staff, contact-indexing means carried by said balance staff and including an electrically insulating portion and an electrically conducting portion, an index assembly having a shaft portion carrying a pinion and having a pivot at one end thereof, a metal hub portion carrying contact means and indexing means and having a pivot at one end, the other end of one of said hub and shaft portions being received in a recess in the other end of the other of said hub and shaft portions and secured thereto by an insulating adhesive.

12. The apparatus of claim 11 wherein said contact means is a first toothed wheel and said indexing means is a second tooth wheel.

13. The apparatus of claim 12 wherein said first toothed wheel has unsymmetrical teeth having one edge longer than the other edge, said shorter edges of said teeth being engaged by said electrically conducting portion of said contact-indexing means.

14. The apparatus of claim 13 wherein said first toothed wheel has unsymmetrical teeth with one generally radial side engageab-le by said electrical-1y conducting portion.

15. The apparatus of claim 14 wherein said generally radially toothed sides are undercut.

16. The apparatus of claim 14 wherein the teeth of said first toothed wheel have rounded tips which are periodically engaged by said electrically conducting portion.

17. A contact-indexing device for an electric watch comprising as oscillating balance stafi, contact-indexing means carried by said balance stafi and including an electrically insulating portion and an electrically conducting portion, an index assembly having a shaft portion carrying a pinion and having a pivot at one end thereof, a metal hub portion carrying a first toothed contact wheel and a second toothed indexing wheel and having a pivot at one end, the other end of one of said hub and shaft portions being received in a recess in the other end of the other of said hub and shaft portions and secured thereto by an insulating adhesive, salid first toothed wheel having unsymmetrical teeth having one edge longer than the other edge, said shorter edges of said teeth being engaged by said electrically conducting portion of said contact-indexing means, the teeth of said first toothed wheel having rounded tips which are periodically engaged by said electrically conducting portion.

18. A contact index system for an electric watch having a coil carried by a balance assembly mounted in the train carrying watch frame and arranged for periodic energization from a battery, comprising, an index assembly including shaft and hub portions, an insulated adhesive joining said hub and shaft portions, said hub portion carrying contact and indexing means, contact means mounted on said balance assembly for periodic engagement and electrical connection with said index assembly, means engaging the lower end of said hub portion and establishing electrical connection between said index assembly and one terminal of said battery, and means engaging said balance assembly and establishing electrical connection therewith to permit periodic conneoti-on of said index assembly to the other terminal of said battery.

19. A contact index system as set about in claim 18 wherein said shaft portion carries an index pinion in electrical and mechanical contact with the train of said watch, and a gear carried by said hub portion and electrical-ly connected to said means. engaging said hub portion, said gear being periodically engaged by said contact means.

20. A contact index system as set out in claim 19 wherein said contact means in insulated from said balance assembly.

21. A contact index system for an electric watch having a coil carried by a balance assembly mounted in the train carrying watch frame and arranged for periodic energization from a battery, comprising, an index assembly being electrically insulated from said frame and from said train, contact means mounted on said balance assembly for periodic engagement and electrical connection with said index assembly, means engaging said index assembly and establishing electrical connection between said index assembly and one terminal of said battery, and means engaging said balance assembly and establishing electrical connection therewith to permit periodic connection of said index assembly to the other terminal of said battery, said index assembly comprising a pinion and a gear, said pinion being electrically insulated from said gear, said index assembly comprising a shaft carrying said pinion and having a pivot at one end thereof journaled in a jewel, a metal hub carrying said gear and having a pivot journaled in a jewel, the other end of said shaft being received in a recess in said hub and secured thereto by an insulating adhesive.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Gen-man application 1,080,030, printed April 14, 1960. 

1. A CONTACT-INDEXING DEVICE FOR AN ELECTRIC WATCH COMPRISING AN OSCILLATING BALANCE STAFF, AN INDEX ASSEMBLY INCLUDING UPPER AND LOWER PORTIONS, AN INSULATING ADHESIVE JOINING SAID PORTIONS SAID UPPER PORTION CARRYING A PINION IN ELECTRICAL AND MECHANICAL CONTACT WITH THE GEAR TRAIN, THE LOWER PORTION CARRYING A TOOTHED INDEX WHEEL ADAPTED TO BE DRIVEN BY SAID BALANCE STAFF, A ROLLER ON SAID BALANCE STAFF, AN INDEX AND CONTACT MEANS MOUNTED ON SAID ROLLER, AND INCLUDING AN ELECTRICALLY INSULATING CAM MEMBER AND AN ELECTRICALLY CONDUCTING CONTACT, SAID INDEX AND CONTACT MEANS ENGAGING SAID INDEX WHEEL AS SAID BALANCE STAFF OSCILLATES TO IMPART STEP-BY-STEP ADVANCEMENT THERETO IN ONE DIRECTION, SAID CONTACT ELECTRICALLY ENGAGING SAID INDEX WHEEL DURING AT LEAST A PORTION OF THE OSCILLATION WHICH CAUSES SAID ADVANCEMENT, SAID CAM ENGAGING SAID INDEX WHEEL DURING THE REVERSE OSCILLATION WHICH CAUSES NO NET ADVANCEMENT, SAID CAM MEMBER COMPRISING AN ELECTRICAL INSULATING MEMBER HAVING A CURVATE SIDE AND BEING ENGAGED WITH SAID CONTACT ON ANOTHER SIDE, AND MEANS ESTABLISHING CONTACT WITH THE LOWER END OF SAID LOWER PORTION OF SAID INDEX ASSEMBLY. 